You might almost feel sorry for David Cameron, as John Major's bastards return. Zombie politicians of yesteryear are assembling outside Cameron's door seeking to destroy him for no other reason than that's their nature. Out-of-office politicians yearning to be back among the living, full of unspent ambition – the haughty Michael Portillo, the deluded Nigel Lawson – are off the leash.

This time there is no pretence: they want out of the European Union now. The Times reports up to half Tory MPs agree. That's the result of years of selection of Tory candidates by dwindling Eurosceptic local parties, where no one slightly pro-European had a chance. No one under 45 has heard anything but most politicians – Labour and Tory – talk of approaching Europe as if it were an enemy with red lines not to be crossed and victories to be won.

Cameron told the Global Investment Conference on Thursday that he could win "fundamental reform" in Europe, which he could then use to sway voters in a referendum in 2017. He thought he'd shot Ukip's fox – and his own Liam Foxites – with that promise in January, but throwing them a bone only whetted their appetite. When he said on Thursday that it "is in Britain's interest to remain the country that is uniquely well-connected to the world", this platitude suddenly sounded disturbingly radical. He has become the thin blue line between his party and Ukip.

Lawson and Portillo dismiss any chance of more than "minimal renegotiation". No reform will ever be enough red meat for them, however hard he tries. Cameron has deliberately fudged what he means, special UK optouts or universal reforms for all: on Thursday he spoke of both. Germany's Angela Merkel seems somewhat receptive, according to Charles Grant of the Centre for European Reform. The working time directive is a sceptic totem that could be rejigged, since many countries don't abide by it. But the UK will get no optouts, and any universal reforms must be small enough not to need treaty change.

The EU is out of favour – no surprise in a crisis worsened by austerity policies that leave rich Germany angry at paying for poor nations, and poor countries outraged at what is imposed on them in the name of a failed economic theory. No growth and – as Douglas Alexander, Labour's shadow foreign secretary, points out – of 27 commissioners, not one commissioner for growth.

Voices on many sides call for a referendum. On these pages, some of an anarcho-conservative tendency always hate institutions, while great pro-Europeans think they can lance the boil, naively hoping reason will prevail. On the left, some want out – seeing the EU as a conservative force in need of break-up. Calling for a referendum is always popular: people tend to want one. How can you deny people a voice? Isn't that an elite conspiracy?

In Scotland Labour's answer to the SNP's demand for an exit referendum was always this: if you want independence, vote SNP. In Westminster elections, taking that clear stand has worked. On the EU referendum, Labour stands equally firm: if you want to vote to get out of Europe, vote for a party that wants out. Alexander has always said: "Reform, not exit." Labour is 100% committed to staying in – but change is essential.

No one need support the EU's errors – the madness of the Strasbourg parliament, paying the common agricultural policy subsidy to the Queen, or the serious lack of a growth plan. But reasons to stay are blindingly clear. US banks and financiers only stay in the City as a gateway to the EU. Japanese car-makers are only here to trade in the EU. President Obama sent an envoy to warn Cameron that a "bridge" to the US was useless if the UK were outside the EU. Cameron presides over the G8 soon, where a long needed EU-US trade deal will bring tariffs tumbling: the UK alone can never win such a deal.

Peace seems a feeble reason to stay in. If prosperity raises a hollow laugh now, it won't soon. Trading with the EU from outside means obeying every rule with no seat at the rule-making table. Europe's future looks unstable, with political indignation everywhere demanding radical institutional response: how could we not be there? If we left, the same isolationism would sweep us out of the European human rights convention too. Do we want to be Belarus?

The referendum dilemma is brutal. Labour is staunch on staying in Europe, so why offer a vote on something it passionately opposes? Hold the line and hope to win through honesty and conviction, obliging people to vote on Europe in the general election. That's where democratic legitimacy lies. Labour hasn't said "never" because no one knows what might befall the EU project. But as shadow cabinet members say, if Labour fails to change the conversation and make the economy, growth and jobs the great decider in 2015, it will have failed anyway.

Here's the dangerous paradox: if Labour bends under pressure and agrees to a 2017 in/out referendum, Britain will leave the EU. After losing an election, the Tories under a Europhobe leader will fight for "out" with all the might of their stampeding press: a mid-term Labour government advocating "in" would be at its weakest. The irony is that if Cameron won the next election, he might be strong enough to pull off a "yes" vote. That's why, for the sake of the country as well as for its own reputation, Labour sticks to its "no referendum" policy. Ed Miliband does not want to be the prime minister to take Britain out of Europe into the wilderness.

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